JPH11186089A - Capacitor and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new type of small-sized organic film capacitor which is small in dielectric loss tangent and leakage current and has large capacity, and its manufacture. SOLUTION: A small-size and large-capacity film capacitor small in dielectric loss tangent and leakage current can be made, by forming a good quality polycarbonic acid resin dielectric film 2 on the surface of an etched aluminum foil electrode 1 which is roughened conductor electrode by electrodeposition, using high polymer solution in which an interface activator is added, and then heat-treating it to harden the dielectric film 2, and furthermore, forming a first polypyrrole layer 3 and a second polypyrrole layer 4 which are conductor layers as counter electrodes and a collector layer 5 on the surface of the dielectric layer 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to a capacitor used for an electronic circuit of an audio device and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, devices have become smaller, thinner and lighter.
With the increase in the density and digitalization of electric device circuits, there is an increasing demand for miniaturization, higher performance, and higher reliability of electronic components. Under such circumstances, there is a strong demand for a capacitor having a small size, a large capacity, and a low impedance in a high frequency region.

As a capacitor having a low impedance in a high frequency region, there is a film capacitor using an organic film as a dielectric, but the dielectric constant of the dielectric is as small as 2 to 3 and the thinning is limited to about 2 μm. Therefore, there is a problem that the shape becomes large and the price becomes high in order to obtain a high capacitance.

On the other hand, an aluminum electrolytic capacitor using an aluminum oxide film as a dielectric has a small size and a large capacity, but has a drawback that impedance and dielectric characteristics in a high frequency region are inferior to those of the above-mentioned film capacitors.
Therefore, in order to improve high-frequency characteristics, aluminum solid electrolytic capacitors have been developed in which the driving electrolyte portion of the aluminum electrolytic capacitor is replaced with a solid material having higher conductivity, such as manganese dioxide or polypyrrole. However, in any case, it is difficult to use an aluminum electrolytic capacitor in an AC circuit because the dielectric oxide film has polarity.

Furthermore, a new type of small-sized and large-capacity film in which a polyimide film is formed on an etched aluminum foil surface by an electrodeposition method instead of an aluminum oxide film, and a conductive polymer is formed on the surface. A method of manufacturing a capacitor is also provided (for example, see
-87312). The present invention is intended to increase the capacitance while maintaining the non-polarity and low dielectric loss tangent of a polyimide film as a dielectric.

[0006]

However, in the above invention, an organic solvent such as dimethylformamide or methanol is used as a solvent for the polyamic acid salt solution when forming the polyimide film. Applying a voltage to an electrodeposition solution containing a large amount of such an organic solvent has a problem in safety, and it is necessary to consider the harmfulness of the organic solvent to the human body. Furthermore, it is often unsuitable for industrial mass production, which is more expensive than water.

Accordingly, the present inventors have developed a conductive electrode obtained by roughening a polyacrylic acid resin dielectric, which is a typical polycarboxylic acid resin, using an aqueous electrodeposition solution which is industrially easy to use. A capacitor formed on the surface and provided with a counter electrode on the surface of the dielectric layer and a method of manufacturing the same have been proposed (Japanese Patent Application Laid-Open No.
-115767).

In the method of the present invention, a hole having a large aspect ratio (pore diameter: 1 to 3 μm, hole length: 30 to 50)
A polycarboxylic acid-based resin is formed on the surface of an etched aluminum foil (thickness: about 100 μm) having a large number of μm), and various evaluations of the characteristics as a capacitor have been made. As a result, there remains a problem that the disadvantage that the leakage current is large must be improved.

One of the causes of the large leakage current is considered as follows. The solvent water used in the electrodeposition solution of the present invention has a higher surface tension than an organic solvent such as methanol. Comparing the surface tension numerically,
Water: 72.6 dyn / cm (20 ° C.), methanol: 2
2.6 dyn / cm (20 ° C.), ethanol: 22.3
dyn / cm (20 ° C.), dimethylformamide: 3
5.2 dyn / cm (25 ° C.), N-methylpyrroline: 41.0 dyn / cm (25 ° C.), and water has an extremely large surface tension among various solvents. As described above, since the aqueous electrodeposition liquid has a large surface tension, there is a possibility that the wettability to the etched aluminum foil is poor or the liquid does not easily penetrate deep into a fine hole having a large aspect ratio. When such a phenomenon occurs, it can be expected that the thickness of the electrodeposited polymer dielectric thin film becomes non-uniform, pinholes are easily generated, and the leakage current increases.

An object of the present invention is to solve the above-mentioned conventional problems and to provide a new type of film capacitor having a small leakage current and a small dielectric loss tangent, a small size and a large capacity, and a method of manufacturing the same.

[0011]

According to the present invention, there is provided a capacitor having a polymer dielectric thin film formed by electrodeposition on the surface of a roughened or porous conductive electrode. A conductive layer as a counter electrode on the surface of the polymer dielectric thin film, wherein the polymer dielectric thin film is electrodeposited using a polymer solution to which a surfactant is added. And

The roughened conductor electrode is preferably an etched aluminum foil. It is also characterized in that the polymer dielectric thin film is a polycarboxylic acid-based resin.

As the surfactant, a fluorine-based surfactant is suitable. In order to achieve the above object, a method for manufacturing a capacitor according to the present invention comprises a step of adding a surfactant to a polymer solution, and electrodepositing a polymer thin film on a roughened or porous conductor electrode surface. And a step of subjecting the dielectric thin film to a hardening reaction by performing a heat treatment, and a step of forming a conductor layer as a counter electrode on the surface of the dielectric thin film.

As the surfactant, a fluorine-based surfactant is suitable for the method for producing a capacitor of the present invention.

[0015]

DETAILED DESCRIPTION OF THE INVENTION The invention according to claim 1 of the present invention comprises a polymer dielectric thin film formed by electrodeposition on the surface of a roughened or porous conductor electrode, Since it has a conductor layer as a counter electrode on the surface of the dielectric thin film, since the polymer dielectric thin film is electrodeposited using a polymer solution to which a surfactant is added,
It has a small number of pinholes, has a uniform film thickness, and has the effect of increasing the adhesion to the conductor electrode.

[0016] The invention described in claim 2 of the present invention provides:
Since an etched aluminum foil having a large surface area is used as the roughened conductor electrode, it has an action suitable for increasing the capacitance of the capacitor.

[0017] The invention according to claim 3 of the present invention provides:
Since polycarboxylic acid resin is used as the polymer dielectric thin film, it is possible to efficiently form a thin film that follows an electrode surface with a complicated surface shape such as a conductor that has been roughened or porous by electrodeposition. Has an action.

Further, the invention according to claim 4 of the present invention provides:
Since the surfactant is a fluorine-based surfactant, it has an effect of becoming a capacitor having a high-quality polymer dielectric film.

The invention according to claim 5 of the present invention provides:
A step of adding a surfactant to the polymer solution, a step of electrodepositing a polymer thin film on the surface of the roughened or porous conductor electrode, and a step of performing a heat treatment to cure the dielectric thin film. And forming a conductive layer as a counter electrode on the surface of the dielectric thin film, so that a capacitor having a high quality dielectric having a uniform film thickness with few pinholes can be manufactured.

The invention according to claim 6 of the present invention provides:
Since the surfactant is a fluorine-based surfactant, it has an effect of significantly lowering the surface tension of the polymer solution.

(Embodiment 1) An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram of a cross section of a capacitor described in this embodiment, and FIG. 2 is a flowchart showing a method of manufacturing the capacitor described in this embodiment.

First, the structure of a target capacitor is shown in FIG.
This will be described in detail with reference to FIG. In the figure, reference numeral 1 denotes an etched aluminum foil electrode having an average pore diameter of 2 μm generated by etching and having a surface area increased to about 30 times by roughening. A polycarboxylic acid-based resin thin film 2 as a dielectric is formed by electrodeposition using a polymer solution to which a surfactant is added so as to follow the surface shape of the electrode 1. The counter electrode of the etched aluminum foil electrode 1 is composed of a current collector layer 5 adhered to the first polypyrrole layer 3 and the second polypyrrole layer 4 of a conductive polymer so as to collect current. . Reference numeral 6 denotes an epoxy resin attached for insulating the electrodes. Then, lead wires are provided on the two electrodes shown in this figure, and they are packaged with epoxy resin (not shown).
This is the configuration of the capacitor of the present embodiment.

The term "polycarboxylic acid resin" as used herein means a resin having at least one carboxylic acid group in the main chain or side chain of a polymer. For example, polyacrylic acid, polymethacrylic acid, and the like. Of course, it is needless to say that copolymers of these or partially esterified ones can also be used. Preferably, an amino resin-based curing agent such as melamine is mixed and the insulating property is improved by a three-dimensional crosslinking reaction at the time of heat treatment. Among these, a polyacrylic acid resin which is water-soluble and excellent in workability, and excellent in adhesiveness to aluminum and flexibility is suitable for this purpose.

Next, a method of manufacturing the above-structured capacitor will be described in detail with reference to FIG.

First, the step of synthesizing the polymer solution for electrodeposition in step 1 will be described. The aqueous solution containing the polycarboxylic acid used was an emulsion solution containing 10% by weight of solid content, 86% by weight of ion-exchanged water, and 4% by weight of butyl cellosolve. The solid content used here was a mixture of a copolymer of polyacrylic acid and polymethacrylic acid (molecular weight: about 20,000) (main ingredient) and a melamine resin (curing agent) in a weight ratio of 7: 3. . When dispersing the solids in the liquid, 50% of the carboxylic acid groups in the solids are neutralized by adding an appropriate amount of triethylamine to improve dispersibility, as is often done by the anion electrodeposition method. Was.

Next, in step 2, 100 ppm of a fluorinated surfactant was added to the polymer solution synthesized in step 1. The surfactant used at this time was a perfluoroalkyl alkoxylate (product name: FC-1713M). As described above, the surface tension of the solution is 68 dyn simply by adding a small amount of the surfactant to the aqueous polymer solution.
/ Cm to 23 dyn / cm. for that reason,
The wettability of the electrodeposition liquid to the etched aluminum foil was significantly improved.

It should be noted that the surfactant is not limited to the fluorine-based one as described above, and it is needless to say that silicon-based and hydrocarbon-based surfactants also exert their effects. Also,
As a result of examining a large number of surfactants, it was found that a fluorine-based surfactant as shown in Step 2 was most suitable for the purpose of the present invention. As used herein, the fluorine-based surfactant includes ammonium salts of perfluoroalkylsulfonic acid, potassium salts of perfluoroalkylsulfonic acid,
Sodium salts of perfluoroalkylsulfonic acid, perfluoroalkylpolyoxyethylene ethanols,
It refers to fluorinated alkyl esters.

Next, the step of electrodepositing the polycarboxylic acid-based resin thin film 2 as a dielectric in step 3 will be described.

First, the electrodeposition solution synthesized in step 1 is put into a cylindrical stainless steel container (cathode) having a diameter of 80 mm.
Next, the etched aluminum foil electrode 1 to which a lead wire was attached by welding was used as a dielectric forming portion (area: 10 mm × 10 mm) and immersed in an electrodeposition solution to form an anode.

Then, a current was applied between the two electrodes at an applied voltage of 50 V (constant) for 10 minutes to form a polycarboxylic acid-based resin thin film 2 as a dielectric on the surface of the etched aluminum foil electrode 1. In step 3, it was found that the polycarboxylic acid-based resin thin film 2 could be formed uniformly to the inner side of the hole due to the effect of the addition of the surfactant. Also,
The size of bubbles generated by the electrolysis of water at the time of applying a voltage was also reduced by adding a surfactant. This makes it possible to suppress the generation of pinholes in the polycarboxylic acid-based resin thin film 2.

It is needless to say that the thickness of the polycarboxylic acid-based resin thin film 2 can be adjusted by changing the magnitude of the applied voltage, the length of the electrodeposition time, the number of times of electrodeposition, and the like in Step 3.

Next, in step 4, the sample on which the dielectric layer was formed in step 3 was washed with water, dried at 80 ° C. for 20 minutes, and heat-treated at 180 ° C. for 30 minutes to obtain a melamine resin and a polycarboxylic acid-based resin. A curing reaction was performed with the resin. Also in this step, the addition of the surfactant improved the leveling effect of the film during drying and heat treatment.

Next, in step 5, the element is set to 1.0 m
ol / l of pyrrole in ethanol and 1.0 mol / l
The operation of alternately immersing in 1 l of an aqueous solution of ammonium persulfate for 2 minutes was repeated three times to form a first polypyrrole layer 3 which was a chemically oxidized and polymerized film of polypyrrole.

Subsequently, in step 6, the element having the first polypyrrole layer 3 formed thereon was replaced with 1 part of pyrrole, 1 part of a 40% by weight aqueous solution of sodium butylnaphthalenesulfonate and 40 parts of distilled water in a cylindrical stainless steel container. The mixture was then immersed in a mixed solution to form an anode, a cylindrical stainless steel container was used as a cathode, and electrolytic polymerization was performed between the two electrodes at a constant current of ^2.5 mA / cm ² for 30 minutes to form a second polypyrrole layer 4. Formed.

Next, in step 7, a current collector layer 5 is formed by applying a conductive material such as colloidal carbon or silver paint to the element. Thus, a counter electrode composed of the first polypyrrole layer 3 and the second polypyrrole layer 4 collected by the current collector layer 5 is formed. Here, a lead wire was soldered to complete the counter electrode.

Further, in step 8, the capacitor of the present embodiment was completed by packaging with an epoxy resin (not shown).

(Performance Study 1) The distributions of the dielectric loss tangent of the capacitor of the first embodiment and the capacitor of the comparative example obtained as described above are shown in FIGS. 3A and 3B, respectively.
The capacitor of the comparative example was manufactured by the same method as that of the first embodiment except that the surfactant was not added to the polymer solution in step 2 of the first embodiment. In each case, a total of 15 pieces were manufactured, and variations in dielectric loss tangent were compared.

The capacitance was not significantly different from that of the first embodiment and the comparative example.
The distribution was in the range of 5 to 0.80 μF / cm ² .

As apparent from FIGS. 3 (a) and 3 (b), a high-quality dielectric having no pinholes was able to be formed in the case where the surfactant was added as compared with the case where no surfactant was added. A large number of capacitors with small size can be manufactured, and the variation is small.

Table 1 shows an example of the electrical characteristics of the capacitors of the first embodiment and the comparative example.

[0042]

[Table 1]

As is apparent from Table 1, the capacitor in which the surfactant was added to the electrodeposition solution of the polymer solution as in the first embodiment of the present development has higher quality than the comparative example in which the surfactant was not added. Since the dielectric film can be formed, the dielectric loss tangent and the leakage current are reduced.

[0044]

As described above, the capacitor according to the present invention has a small number of pinholes and a uniform film thickness by electrodeposition using a polymer solution containing a surfactant.
In addition, it has a polymer dielectric thin film having high adhesion to the conductor electrode, and exhibits an effect of reducing dielectric loss tangent and leakage current.

Since an etched aluminum foil having a large surface area is used as the roughened conductor electrode, the capacitance of the capacitor can be easily increased.

Further, since a polycarboxylic acid resin is used as the polymer dielectric thin film, a thin film that follows an electrode surface having a complicated surface shape, such as a conductor roughened or porous by an electrodeposition method, can be used. This has the effect that a capacitor that can be formed efficiently, has a small size, a large capacity, and is excellent in heat resistance can be realized.

When a fluorine-based surfactant is used as the surfactant, the surface tension of the polymer solution can be greatly reduced, and a small and large-capacity film capacitor having a small dielectric loss tangent and leakage current can be realized. .

Further, the method for producing a capacitor according to the present invention comprises the steps of adding a surfactant to a polymer solution, and electrodepositing a polymer thin film on a roughened or porous conductive electrode surface. A step of subjecting the dielectric thin film to a hardening reaction by heat treatment; and a step of forming a conductive layer as a counter electrode on the surface of the dielectric thin film. Can be formed, so that a capacitor having a small dielectric loss tangent and a small leakage current can be manufactured.

When a fluorine-based surfactant is used as the surfactant, the surface tension of the polymer solution can be greatly reduced, and a small and large-capacity organic film capacitor having a small dielectric loss tangent and leakage current can be manufactured. it can.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a cross section of a capacitor according to a first embodiment of the present invention.

FIG. 2 is a flowchart of a method for manufacturing a capacitor according to the first embodiment of the present invention.

3A is a distribution diagram of a dielectric tangent of a capacitor according to a first embodiment of the present invention; FIG. 3B is a distribution diagram of a dielectric tangent of a capacitor according to a comparative example;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 Etched aluminum foil electrode 2 Polycarboxylic acid resin thin film (dielectric layer) 3 First polypyrrole layer 4 Second polypyrrole layer 5 Current collector layer 6 Epoxy resin (for insulation)

Claims (6)

[Claims] 1. A polymer dielectric thin film formed by electrodeposition on the surface of a roughened or porous conductive electrode, and a conductive layer as a counter electrode on the surface of the polymer dielectric thin film. Wherein the polymer dielectric thin film is electrodeposited using a polymer solution to which a surfactant is added. 2. The capacitor according to claim 1, wherein the roughened conductor electrode is an etched aluminum foil. 3. The capacitor according to claim 1, wherein the polymer dielectric thin film is a polycarboxylic acid resin. 4. The capacitor according to claim 1, wherein the surfactant is a fluorine-based surfactant. 5. A step of adding a surfactant to a polymer solution; a step of electrodepositing a polymer dielectric thin film on a roughened or porous conductive electrode surface; A method of manufacturing a capacitor, comprising: a step of curing a dielectric thin film; and a step of forming a conductive layer as a counter electrode on the surface of the polymer dielectric thin film. 6. The method according to claim 5, wherein the surfactant is a fluorine-based surfactant.